1. Field of the Invention
An aspect of this disclosure relates to a method of affixing a heat transfer sheet.
2. Description of the Related Art
In a semiconductor device production process, plasma processing such as etching or film deposition is performed many times on a semiconductor wafer (which is hereafter referred to as a “wafer”) that is an object to be processed.
In a plasma processing apparatus for performing plasma processing, a focus ring is provided on a table on which a wafer is placed such that the wafer is surrounded by the focus ring. The focus ring causes the distribution range of plasma generated above the wafer to expand to cover not only a space above the wafer but also a space above the focus ring so that plasma processing is performed uniformly on the entire surface of the wafer.
During plasma processing, the wafer and the focus ring are exposed directly to plasma and as a result, their temperature rises. Therefore, the temperature of the table is controlled to control the temperature of the wafer as well as the temperature of the focus ring.
Here, when the efficiency of heat transfer between the table and the focus ring is low, it is difficult to control the temperature of the focus ring. For this reason, a heat transfer sheet made of, for example, silicon rubber is provided between the table and the focus ring to improve the contact between them and thereby improve the heat transfer efficiency.
When affixing the heat transfer sheet to the focus ring, air bubbles may enter between them. The entered air bubbles function as a heat insulating layer that reduces the efficiency of heat transfer between the table and the focus ring, and therefore make it difficult to control the temperature of the focus ring. To solve this problem, Japanese Laid-Open Patent Publication No. 2008-171899 discloses a technology where a vacuum is generated after the heat transfer sheet is affixed to concentrate fine air bubbles and then the pressure is returned to the atmospheric pressure to remove the concentrated air bubbles.
However, with the method of Japanese Laid-Open Patent Publication No. 2008-171899, air bubbles cannot be completely removed depending on how the heat transfer sheet is affixed and it is difficult to achieve sufficient heat transfer efficiency between the table and the focus ring.